1. Field of the Invention
The present invention relates to a stereoscopic display device, and more particularly, to an electrically-driven liquid crystal lens, which can be switched between a convex lens and a concave lens by changing an optical path difference based on an electric field application manner, and a stereoscopic display device using the same.
2. Discussion of the Related Art
At present, services for rapid dissemination of information, on high-speed information communication networks, have developed from a simple “listening and speaking” service, such as current telephones, to a “watching and listening” multimedia type service based on digital terminals used for high-speed processing of characters, voice and images, and are expected to be ultimately developed into cyberspace 3-dimensional stereoscopic information communication services enabling virtual reality and stereoscopic viewing free from the restrains of time and space.
In general, stereoscopic images representing 3-dimensions are realized based on the principle of stereo-vision via the viewer's eyes. However, since the viewer's eyes are spaced apart from each other by about 65 mm, i.e. have a binocular parallax, the left and right eyes perceive slightly different images due to a positional difference therebetween. Such a difference between images due to the positional difference of the eyes is called binocular disparity. A 3-dimensional stereoscopic image display device is designed on the basis of binocular disparity, allowing the left eye to view only an image for the left eye and the right eye to view only an image for the right eye.
Specifically, the left and right eyes view different 2-dimensional images, respectively. If the two different images are transmitted to the brain through the retina, the brain accurately fuses the images, giving the impression of real 3-dimensional images. This ability is conventionally called stereography, and a stereoscopic display device is obtained by applying stereography to a display device.
Technologies for displaying the above-described 3-dimensional stereoscopic images may be classified into a stereoscopic display method using binocular disparity, and a volumetric measurement method using perception per volumetric unit. As an example of the volumetric measurement method, there is an Integral Photography (IP) display method wherein integrated images such as holograms are perceived. In the IP display method, a microlens array is used that does not require a user to wear glasses.
Such an IP display method using a microlens array, as a representative technology for realizing 3-dimensional images, was first proposed by Lippman in 1908, but has not attracted considerable attention due to a limit in technologies of display devices. Recently, in conjunction with developments in high-resolution display devices, an IP display method has been actively researched.
Hereinafter, a conventional stereoscopic display device will be described with reference to the drawing.
FIG. 1 is a schematic view illustrating a conventional IP type stereoscopic display device.
As shown in FIG. 1, a conventional IP type stereoscopic display device includes a display device 10 and a lens array 20 consisting of microlenses as unit lens.
Here, assuming that the microlenses of the lens array 20 have a focal distance f, if a distance a between the display device 10 and the lens array 20 is determined, a distance b between the lens array 20 and a position where an integrated image is formed can be calculated by the following Equation.
                                          1            a                    +                      1            b                          =                  1          f                                    Equation        ⁢                                  ⁢        1            
In the stereoscopic display device, if the shape of the microlenses of the lens array 20 (i.e. the convexity of a lens plane) (here, the lens array 20 comprises a plurality of lens 21) is determined, the focal distance f is determined based on the plane shape of the microlenses. Since the distance a between the lens array 20 and the display device 10 within the stereoscopic display device is set to a predetermined value, the distance b between the lens array 20 and the integrated image can be determined by the focal distance f and the distance a between the lens array 20 and the display device 10.
However, the above-described conventional IP type stereoscopic display device has the following problems.
When forming a lens array having a curved lens plane, uniform control on a per region basis of the curved lens and attachment/alignment between the lens array and a display device therebelow are difficult, resulting in deterioration in visual sensitivity.
Therefore, as part of the effort to change the shape of the lens array, there has been introduced an electrically-driven liquid crystal lens based on a difference in the refractive indexes of liquid crystals under the influence of an electric field. The electrically-driven liquid crystal lens does not require processing of a lens plane and can be realized via a simplified electrode arrangement and voltage application, thereby preventing problems due to lens processing.